Spacing means for wall sections of flame tubes



F Q Q Q M rch 5 F. D. M. WILLIAMS ET AL 2,670,601

SEACING MEANS FOR WALL SECTIONS OF FLAME TUBES Filed 001;. 17, 1950 2 Sheets-Sheet l P G 6 I A 'IIIII I'll! rllll'll 7 INVENTORS F.0. M. WILLIAMS 0, z. Mann/501v March 2, 1954 F. D. M- WILLIAMS ET AL SPACING MEANS FOR WALL SECTIONS OF FLAME TUBES Filed Oct. 17, 1950 2 Sheets-Sheet 2 mvmrons f. D. M. W/LL/AMS 0. f. MORE/SON Patented Mar. 2, 1954 UNITED" STATES PATENT OFFICE SPACING MEANS FOR WALL SECTIONS OF FLAME TUBES Application October 17, 1950, Serial No. 190,462

4 Claims.

This invention relates to spacing means for the wall sections of flame tubes more particularly for use in gas turbine engines.

The development of gas turbines has necessitated the development of combustion chambers with means to coo-l the walls and thereby limit the distortion or damage that might result from the intense heat generated within the chambers. To this end it is customary to contain the combustion within a flame tube situated, in spaced relationship, inside the outer casing of the combustion chamber; and to cool the walls of the said flame tube by a stream of air through the annular space between the flame tube and the casing, and by a film of air introduced to flow internally over the walls of the fiame tube, thereby ailording some degree of insulation from the heat of combustion.

A well known form of flame tube construction consists of a plurality of circular or annular sections arranged coaxially, the cross-sectional area of the upstream end of any section being substantially greater than the area of the downstream end of the section immediately preceding it. The ends of adjacent sections overlap and are held in correct radial relationship by spacing means in the annulus between the overlapping surfaces. Thus an annular film of air can be introduced, from the cooling air flowing outside the flame tube, to flow over the inner surface of each section.

In co-pending application Serial No. 111,150, dated August 19th, 1949, by W. M. McDonald, now Patent No. 2,645,081, is described a spacing means characterized by the provision of a plurality of openings formed in and arranged around the circumference of at least one of the overlapped or overlapping portions of the sections and spacers formed of sheet metal of a thickness substantially less than the width of the space between the overlapping sections and arranged so that their major surfaces are substantially parallel to the longitudinal axis of the flame tube, and with one edge meeting the flow of air through the said space. Each spacer is secured to the section having the openings at least one side of each opening and secured to the other section opposite the opening, through which opening access to the spacer may be gained to facilitate the securing of the spacer to the other section. It will be understood that in accordance with this construction the flow air through the space between the overlapping portions of the sections is obstructed only by the edge thicknesses of the sheet metal spacers and these edge thickness are disposed partly across the space and partly along it; the latter constituting the parts of the spacers which are attached, in lap joints, to the said other section. The portion of each spacer crossing or spanning the space performs an essential function as a strut, in supporting the sections in spaced relationship, and its presence in the air stream is unavoidable: but the circumferentially disposed portion, forming the lap joint, causes an undesirable obstruction in the space which should be eliminated if possible. The width of the space in question may be of the order of T e" and it will be readily understood that the circumferentially disposed portions of the spacers may occupy a substantial fraction of the annulus unless material of impracticably thin gauge is used.

The object of this invention is to eliminate the obstruction caused by the circumferentially disposed portions of the spacers so that the only impedance to the flow of air through the space is due to the supporting or strut portions of the spacers spanning the space. Other objects and advantages of the invention will be apparent during the course of the following description of three preferred examples of its application.

In the following drawings, forming a part of this specification and in which like reference characters designate like parts throughout the same;

Fig. 1 represents a longitudinal section of a combustion chamber showing the overlapping relationship of adjacent wall sections of the flame tube;

Fig. 2 is a fragmentary perspective view of the spacing means shown in Fig. 1 on an enlarged scale; and

Figs. 3 and 4 are fragmentary sections of alternative forms of spacing means.

In the drawings a tube type combustion chamber is shown but it will be understood that this invention can be applied equally to the annular type of combustion chamber and that the general external shape of the chamber has no bearing upon use of the invention.

Referring to Fig. 1 it will be seen that a name tube H! is mounted in a casing l I and that the air, entering at the upstream end of the combustion chamber as illustrated by the arrows is free to flow through the annular space A between these two components. The flame tube consists of a series of coaxial substantially cylindrical sections, designated by the numerals l2, l3 and I4,- and where adjacent sections overlap the diameter of the upstream and of the downstream section is materially greater than the diameter of the downstream end of the upstream section, and their opposing walls form between them radial spaces I5 through which the cooling air is admitted to flow from the annular space A to the inside surfaces of each section. The radial spaces are maintained by spacers I6 which hold the adjacent sections in spaced relationship to one another.

Fig. 2 shows a typical spacer, in this case between the sections I2 and I3. A circumferentially directed slot I! with smooth rounded ends is cut through the wall of the section I2 at a suitable distance from the circumferential edge I8 at the end of the section I2 which is overlapped by the wall of the larger section I3. The strip of sheet metal thus formed between the slot I7 and the circumferential edge I8 is outwardly depressed to form a substantially U-shaped spacer I3 making face to face contact with the wall of the section IS. The portion of the wall of the section I3 in contact with the spacer l s is locally outwardly depressed to make an excrescence I9, that it is recessed relatively to the adjoining portion of section I3 in a sense away from the end portion of wall section i2 to form a recess I I in the surface of the wall of section I 3 of a depth at least equal to the thickness of the metal of the portion of the spacer IS in the recess. (In practice, in order to insure that the portion of the spacer which is secured to the section I3 is wholly accommodated in the recess, it is advisable to form the excrescence I9 so that it covers an area slightly greater than its area of contact with the circumferentially disposed portion of the spacer I3; this precaution will avoid the necessity of very accurate location of the spacers and the excrescences during manufacture, and will provide some tolerance for errors.) The area. of contact between the spacer I6 and the excrescence I9 may :bejoined by welding, riveting, or other attaching means indicated by the numeral 20. By means of a plurality of such spacers secured to the bottoms of a plurality of recessed portions spaced from each other and arranged perimetrically in proximity to the circumferential edge I8 of the section I2, the end of the larger section I3 is held in proper radial and axial relationship to the smaller section I 2.

From the foregoing description the functioning of the improved construction will be readily apparent. The cooling air flowing through the annular space A in the direction of the arrow enters the section I3 through the radial space I5 and provides adequate cooling of the inner surfaces of the wall thereof downstream of the space. The passage of air through the space I5 is only slightly impeded by the portions of the spacers I6 spanning the said space because the spacers are arranged so that their major surfaces are substantially parallel to the longitudinal axis of the overlapping end portions of the wall sections ofthe flame tube with their edges facing the flow of air through the space. The circumferentially disposed portions of the spacers I I5, accommodated in the recesses inside the excrescences l9, are in effect flush with the inner surface of the section I3 and therefore do not impede the air flowing through the space.

An alternative form of the invention is shown in Fig. 3. In this construction the excrescences I9 .of the arrangement shown in Fig. 2 are replaced by an annular rim 2|, formed in the end of the wall of the section I3 by the circumferentially disposed continuous step or joggle 22; the depth of the joggle is of course the same as the depth of the replaced excrescences I9, so that the circumferentially disposed portions of the spacers attached thereto are in effect flush with the inner surface of the section I3.

In yet another construction shown in Fig. 4 the section I3 .is not depressed .or .joggled outwardly in the neighbourhood of the spacers but a continuous recessed portion is provided by a sleeve 23 overlapping the exterior of the wall of the section and forming an extension to the wall of the section. The spacer I6 is fastened by the attaching means 20 directly to the extension 23 so that the lap joint between the extension and the circumferentially disposed portion of the spacer I6 is level with the outer surface of the section I3. If the thickness of the metal of which the section I3 is made is the same as the thickness of the metal of the section I2 and of the spacer i6, which is a part of the section I2, then the inner surface of the circumferentially disposed portion of the spacer is flush with the inner surface of the section I3 and-the same result is achieved as in the constructions described hereinbefore.

It will be noted that in Figs. 3 and 4 the spacers are not formed at the extreme edge of the section I2 but are outwardly depressed between the slots I? and similar slots I P, so that there is a narrow continuous strip or band of unformed metal between the slots I'I and the edge I8. This type of spacer is to be preferred in constructions such as those depicted in Figs. 3 and 4 to provide an adequate overlap between the sections, not so much at the spacers as between adjacent spacers; the arrangement of the juggled rim or the doubler Produces an otherwise undesirable increase in the width of the space I5, where it is not actually serving to accommodate the circumferentially disposed portions of the spacers.

It will be understood that the forms of the in vention herewith shown and described are to be taken as preferred examples of the same and that similar results could be achieved by forming the spacers in the overlapping section I3 so that the spacers extend inwardly towards the inner section I2. In such an arrangement, of course, the circumferentially disposed portions of the spacers would be be accommodated in inward depressions in the section I2 or by means of an inwardly joggled rim or a doubler attached to the inner surface of the section I2 and extending beyond the edge I8. Furthermore, the invention may be applied to any form of sheet metal spacer disposed with its major surfaces substantially parallel to the direction of air flow and the embodiment of a spacer according to co-pending application Serial No. 111,150 is not to be regarded as restrictive.

Moreover, it is not intended that the application of this invention should be confined to flame tubes of circular cross-section and, although the slots I! and I I have been described herein as circumferentially directed and arranged, the use of such words as circumferential and circus.- ferentially has been dictated by the fact that the flame tubes described are substantially circular and have circumferences. More broadly, to include the application of the invention to flame tubes of both circular and non-circular cross section, it might be said that the slots are arranged perimeterically, since a circumference is a particular form of perimeter.

Various other changes in the shape, size andarrangement of the parts may therefore be resorted to without departing from the spirit of the invention orthe scope of the subjoined claims.

What we claim as our invention is:

1. A flame tube comprising a first wall section, a second wall section having an end portion overlapping and spaced from an end portion of the first wall section, the end portions having a common longitudinal axis and their mutually opposing walls defining a space between them through which air can flow into the second wall section and the flame tube, at least a part of one of the said end portions being recessed relatively to the adjoining portion of the corresponding wall section in a sence away from the other of the said end portions and thus providing a recessed surface, and sheet metal spacers extending between the said end portions and arranged with their major surfaces substantially parallel to the longitudinal axis of the said end portions and with one edge of each spacer facing the flow of air through the said space, each spacer being secured to one of the end portions with a part of a major surface in face-to-face with th said recessed surface, the depth of the recess at the area of contact being about the same as the thickness of the sheet metal of the spacers so that the said parts of their major surfaces are substantially wholly accommodated in the recess and do not impede the flow of air through the said space.

2. A flame tube having in combination a first wall section, a second wall section having an end portion overlapping and spaced from an end portion of the first wall section, the end portions having a common longitudinal axis and their mutually opposing walls forming a space between them through which air can flow into the second wall section, one of the end portions having a plurality of areas recessed relatively to the remaining part of the said end portion in a sense away from the other of the end portions, the recessed areas being spaced from each other and arranged perimetrically around the said end portion, and sheet metal spacers extending between the end portions and arranged with their major surfaces substantially parallel to the longitudinal axis of said portions and with one edge of each spacer facing the flow of air through the said space, each spacer being secured to one of the end portions with a part of a major surface in face-to-face contact with the said re cessed areas, the depth of the recesses being about the same as the thickness of the sheet metal of the spacers so that the said parts of their major surfaces are wholly accommodated in the recesses and do not impede the flow of air through the said space.

3. A flame tube having in combination a first wall section, a second wall section having an end section, at least a part of one of the end portions being recessed relatively to the adjoining portion of the corresponding wall section thus providing a recessed surface, the said recessed surface being formed by a step in the section extending continuously around the perimeter of its end portion, and sheet metal spacers extending between the said end portions and arranged with their major surfaces substantially parallel to the longitudinal axis of said end portions and with one edge of each spacer facing the flow of air through the said space, each of the spacers being secured to one of the end portions with a part of a major surface in face-to-face contact with the said recessed surface, the depth of the said step being about the same as the thickness of th sheet metal of the spacers so that the said parts of their major surfaces are wholly accommodated in the recess and do not impede the flow of air through the said space.

4. A flame tube having in combination a first wall section, a second wall section having an end portion overlapping and spaced from an end portion of the first wall section, the end portions having a common longitudinal axis and their mutually opposing walls forming a space between them through which air can flow into the second wall section, at least a part of one of the end portions being recessed relatively to the adjoining portion of the corresponding wall section and thus providing a recessed surface, the said recessed surface being formed by a wall section extension overlapping the said adjoining portion on the side of the adjoining portion remote from the other end portion, whereby the depth of the recess is the thickness of the said adjoining portion, and sheet metal spacers extending between said end portions and arranged with their major surfaces substantially parallel to the longitudinal axis of said portions and with one edge of each spacer facing the flow of air through the said space, each spacer being secured to one of the end portions with a part of a major surface in face-to-face contact with the said recessed surface, the depth of the recess being about the same as the thickness of the sheet metal of the spacers so that the said parts of their major surfaces are wholly accommodated in the recess and do not impede the flow of air through the said space.

FREDERICK D. M. WILLIAMS. DONALD E. MORRISON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,357,894 Pearsall Nov. 2, 1920 1,661,674 Osborn Mar. 6, 1928 1,996,977 Scheu Apr. 9, 1935 2,268,464 Seippel Dec. 30, 1941 2,549,858 Sforzini Apr. 24, 1951 

